We have shown a relationship between estrogen levels, estrogen production and bone mass in peri- and postmenopausal women. There is also evidence that androgens may influence bone mass in such women. Therefore, as the Steroid Core we wish to continue measurements of hormone levels in the groups of women enrolled in the study and to extend these measurements to black women, twins, and aging men in support of the proposals in the Progra Project. We also wish to confirm our measurements of steroid dynamics in the pre-, peri-, and post-menopausal women whom we have been following.